The present invention relates to an electrode for use in an arrangement for spectro-analytically determining the composition of materials, particularly metallic alloyed materials.
The principles of spectro-analysis are so well known that they need no detailed discussion here. The field which is of primary concern for the present invention is that where an electric spark discharge is passed between a conductive workpiece to be tested and an electrode.
It is known to examine workpieces or similar bodies for their compositions by generating a unipolar or single-polarity pulse or spark discharge between a sample of such workpiece which is in contact with an electrode, and a counterelectrode spaced from the sample. The spark is luminous and emits light in both the visible and ultraviolet spectrum, which light can be then divided into spectral lines each of which is indicative of the presence of an alloying element present in the workpiece, while the intensity of each line represents the quantity or percentage of that component in the material of the workpiece. Thus, a spectrometer working with such a spark-discharge arrangement can perform an exact quantitative and qualitative analysis of the composition of the material of the alloyed workpiece.
Such a spectro-analytical examination finds its most prominent use in the steel-manufacturing and related industries wherein it is very often desired to determine whether or not the alloyed materials being produced or stored conform in their composition to predetermined percentages of various alloying elements. As already mentioned previously, this is accomplished, more often than not, by taking samples from the workpieces the composition of which is to be determined, and by testing such samples in laboratories both qualitatively and quantitatively by means of spectrometers. The sample and the counterelectrode are brought to a high potential differential so that a spark discharge occurs between the sample and the counterelectrode. Then, the luminous emission of the spark discharge is transformed into a spectrum by means of a diffractive grating, which spectrum is then evaluated. The chemical elements which are present in the material of the sample are indicated by the presence of emission or absorption lines at corresponding zones of the spectrum. The intensity of each of the spectral lines is a measure for the percentage of the particular element in the alloyed material, and such percentages can be established in an optical and electronic manner such as by resorting to the use of integrating capacitors.
Inasmuch as a device for producing high potentials is necessary for generating the spark discharge and thus the luminous emission which is then deflected to form the spectrum, it is necessary generally speaking, to attend to complex protective measures so as to protect the operating personnel from the existing high voltages. Inasmuch as a part of the spectral lines to be detected is located in the short-wave ultraviolet region of the spectrum, it is necessary to so construct the arrangement as to be not only secure in terms of the high voltage, but also at least a part of the arrangement which embraces the path of the luminous rays from the spark discharge location to at least the deflective grating must be capable of being evacuated. These requirements have resulted in a situation in which these arrangements, which are designated as quantometers, necessarily have large dimensions and a corresponding weight and, for these reasons, they must be constructed for stationary mounting, that is, they can only be used when immovably mounted in a laboratory.
In addition thereto, there have also been already proposed, for the production of the reflective spectrum, Rowland spectrometers which are possessed of the advantage that the images of the spectrum lines are located in a so-called Rowland circle. In the currently available quantometers, the Rowland circle has a substantial diameter, inasmuch as the so-called primary slit which acts as an ingress pupil and serves to create an image of the spark discharge on the Rowland grating, must be adjustable in its position. One of the primary reasons for selecting the large diameter of the Rowland circle is that the short circular arc in which the primary slit is to be adjusted can be regarded, in the first approximation, as being a straight line, so that the primary slit can be provided in an element mounted on a carrier arm for pivoting eccentrically to the center of the Rowland circle, and the position thereby can be adjusted by pivoting such carrier arm. For this reason, analyzers must have considerable dimensions and used in a stationary manner, even in the event that they are operated exclusively in the visible range of the spectrum and, therefore, the above-mentioned evacuation is dispensed with.
In many instances, however, one is interested in a constant supervision of the composition of the material, wherein only the maintaining of the proper percentage of, for instance, silicone, chromium, molybdenum, and so on is to be examined, that is, the material is to be examined for elements the spectral lines of which to be monitored lie in the visible and long-wave ultraviolet part of the spectrum, so that evacuated arrangements need not be employed. This is, for instance, the case when batches of tied rod material with predetermined proportions of chromium, molybdenum and so on in their material are to be examined for the presence of eroneously sorted rods having materials of different composition, and such improper rods are to be sorted out of the respective batch.
Especially under these circumstances, the testing of each rod by severing a disc-shaped end portion therefrom and testing such severed end portion in a quantometer, is too laborious and expensive a procedure and, from a certain number of the rods upward, it is not economically feasible and thus cannot be resorted to, so that it was heretofore customary under such circumstances to utilize random sampling techniques which, of course, are highly unreliable in most circumstances.
There have also already been proposed hand-held spectroscopic devices to be used for random-sample monitoring without taking samples, which render it possible to approximately examine the composition of the material being examined by visual observation of the spectrum which is deflected by prisms. In this arrangement, however, a very high degree of skill and experience is required for properly associating the respective spectral lines with various elements. Even then, however, the visual perception is inadequate to perceive the variations in the intensities of the various spectral lines, which result from different proportions of the respective element in the material being tested.
The generation of the electric spark discharge may be accomplished by means of bipolar excitement, but under these circumstances, material evaporates both from the sample of the material being tested and from the electrode. Such material then deposits on the sample being tested, on the one hand, but also on the counter-electrode, on the other hand, so that when the next-following sample is being tested, to determine the spectral analysis of such sample, the material previously deposited on the counterelectrode will also produce a spectrum and thus partially influence the spectrum of the material of the sample being tested, so that misleading results, in terms of spectral lines, may be obtained.
In order to avoid evaporation of the material of the counterelectrode, it is further known to trigger a unipolar electric spark discharge, in which a deposition of vaporized material on the electrode can be avoided.
An apparatus of conventional nature which employs this concept is possessed of the above-discussed disadvantages, particularly in view of the fact that a material sample must be taken from the material to be examined, and such sample must be examined in a laboratory by means of the analyzer present therein.
In order to be able to achieve a constant super-vision without sample taking of, for instance, tight bundles of rod material, there has already been proposed an analyzer of the portable type. The details of such a portable analyzer can be found in the above-mentioned commonly owned patent applications. Such a portable analyzer is transported to a storage area where the rods to be tested are stored and then an electric spark discharge is generated between a respective end face of one of the rods and the electrode which is held at a predetermined distance from the end face by means of a sleeve, with resulting formation of a spectrum. Such spectrum is then evaluated and thus all of the above-mentioned rods can be tested in a relatively short period of time.
In the conventional arrangement a hardened area is produced at that region of the rod or other workpiece being examined where the spark discharge jumps over. However, such hardening is most undesirable, especially because, generally speaking, the affected end portions, however short, are unusable during the further machining or other treating of the rods. In principle, these hardened areas could be grinded, milled or otherwise machined away, or the affected end portions could be cut away and discarded. However, under these circumstances, the constant supervision or testing would be rendered prohibitively cumbersome and expensive.
When the electric spark discharge occurs in the ambient atmosphere, the above-mentioned hardening is rendered even more pronounced by the formations of a flowable slag ball at the point of impingement of the spark discharge, which is additionally a preferred and prominant point for the spark discharge to travel to. A result of this is that, in addition to the more pronounced hardening, there obtains as a further undesired effect a reduction in the accuracy of the analysis.
Such hardening also occurred in the prior art where samples are being tested, but did not have any detrimental consequences inasmuch as each of the samples was discarded after the performance of the analysis.